Electrootical image-producing system



Sept. 30, 1930. R. K. POTTER ELECTROOPTICAL `IMAGE PRODUCING SYSTEM 2 Sheets-Shea?l 1 Filed M2My 19, 1928 /Nl/E/vrof? RALPH POTTER Arrow/Ey Sept- 30, 1930. R. K. POTTER ELECTROOPTICAL IMAGE PRODUCING SYSTEM.

Filed Ma';v 19, 1928 Z'Sheets-Sheeft 2 /NvE/vmR RA PH h. PorrER ATTRNE Y i :o maybe a Patented 'Sepa 30, '1930;

RALPH 1; POTTER, or NEw'Yonx,

N. Y., ASSIGNOR'TO AMERICAN TELEPHONE ANI.)

TELEGRAPH COMPANY, A CORPORATION OF NEW YORK ELECTROOPTICAL IMAGE-PRODCIN G SYSTEM I .Application led lay 19,

This invention relates to lelectro-optical image production, and particularly to a carrier current image producing system and to methods of image production in which phase 5 modulation of the carrier current is employed.

The general object of the invention is to control the productionl of an image` by a carrier wave which has been modulated with respect to phase.

Inone embodiment of the invention herein-shown and described, by way of example, a carrier current modulated with respect to phase in accordance with the tone values of successive elemental areas of anobject, is employed to control the actuation of a light controlling element such as a light valve foif` producing the image.

' Instead of employinga single light controlling element, a plurality of such elements may be used for jointly controlling the production of the image, as'in another embodiment of this invention described below. In this embodiment the actuation of one of the light controlling elements is conztrolled by unmodulated current of the carrier reqluency Ind-the actuation of another of the e einen Y is controlled by the modulated carrier current. Eaclrof these elements may be a light valve, or if desired, one lightvalvegand another a primary source of light such as a glow. discharge lamp.' One of the light valves or the glow discharge lamp controls the amount' of light emitted in` accordance with the variations in the instantaneous values of amplitude of the carrier current, while'the other light valve vis -designed so that it opens abruptly for a short interval during each cycle ofthe un-V u modulated current of carrier frequency, the

time of opening being varied in accordance y `wvith the phase variations ofthe modulated carrier current. It isv thus apparent that the amount of light reaching the position at which the image is being`produced'is determined by the portion o f the cycleof the carrier current at which'the opening of the light valve, just mentioned, occurs.

A detailed description of severel embodi.

5o ments .of the invention follows, reference be-A 1928. Serial No. 279,041.

ing made to the accompanying drawing, in which: v

Figures 1, 2 and 3 are circuit diagrams illustrating several embodiments of an electro-optical image producing system in accordance with this invention;

Fig. 4 is a diagram which illustrates the operation of' the image producing system shown in Figs. 2 or 3; and

Fig. 5 is a diagrammatic showing of a circuit for modulating the phase of a carrier wave in accordance with the tone value variations of an object.

.The image producing systems, shown in Figs. 1, 2 and 3 employ the usual apparatus for scanning the elemental areas of a picture or other objectjat the transmitting station and for synthesizing the elemental areasat the receiving station to form an image of the picture or object. Thescanning and synthesizing apparatusV shown in these figures is suitable for picture reproduction. A more detaileddisclosure of this part of the system as applied to picture reproducing is found in Patent 1,606,227 to' J. W. Horton, H. E. Ives and M. B. Long, November 9, 1926, and, as applied to television, in copending application to F. Gray, Serial No. 227,649, filed Oct. 21, 1927.

In Fig. 1 a drum 10 of transparent material, such as glass, has mounted thereon a negative picture representation 1.1, the dev.gree of transparency of which varies in accordance with the'tone values of the elemen- 'tal areas thereof. Thus drum is rotated about its axis and at-the same time moves in thedirection of its axis so that light from a source 12 focused on the picture representation, describes a helical course thereon.4 The synchrodrum 10 is driven by a'motor`13 in nism with a similar drum 14 at the receiv' station which is drum -14 at the driven by a motor 15. The receiving statlon carries an4 element having a light sensitive surface on 'y Awhich the picture is to be reproduced. Thev light transmitted through the negative picture representation 11 reaches a photoelectric cell 16 and causes the amplitude of-the .current in the circuit associated with the photoe'lectric cell to vary in accordance with the variations in tone value of the successively scanned elemental areas of the picture. The

\ image current produced by the photoelectric cell and the carrier current of constant frequency from a source 17 are impressed on a phase modulator 18 to produce a carrier current which is modulated with respect to phase. This phase modulator will be referred to more in detail in connection with Fig. 5. The phase modulated wave is transmitted over a suitable channel 19 such as a Wire line or a radio transmission channel. At the receiving station, the phase modulated wave is' amplied by an electron discharge amplifier 2O and impressed across a portion of the Winding of potentiometer 21. Current from a source 22 having the same frequency characteristics as that of the source 7 at the transmitting station is impressed on another portion of the winding of potentiometer 21. Instead of employing a separate source of carrier current 22 at the re ceiving station, carrier current may be transmitted from source 17 at the transmitting station. The mid terminal of the primary winding of transformer 23 is connected to the mid terminal of potentiometer 21 While the end terminals of the transformer Winding are connected to the variable contacts of the potentiometer. The phase and amplitude of the current from the source 22 are so adi justed that when a black element of the negative picture representation .is being transmitted, the current from this source flowing in the primary windin of transformer 23 is equal in amplitude an opposite in phase tol the current from amplifier 20 flowing in this transformer winding. For this condition no current is transmitted throu h amplifier 24 to light valve 25 and no lig t from source 26 reaches the light sensitive surface mounted on the revolving drum\ .14. The light valve 25 maybe of the type disclosed in U. S. Patent 1,638,555, granted to E. C.

Wente, August 9, 1927. When the tone value y of the picture element in the path of the light beam from source 12 changes from black to some other, tone value, a phase displacementtakes place in the Wave transmitted over channel 19 and impressed on the primary Winding of transformer 23. Current proportional to the vector sum of the current from the source 22 flowing in the primary winding of transformer 23 and the phase modulated current transmitted over thev channel 19 flowing in this winding of transformer 23 is impressed on the light valve 25, thus opening the light valve and exposing lthe light sensitive surface to light from the source 26. Since the change in phase of the wave transmitted over channel 19 varies in accordance with the change in tone value of the elemental areas of the negative picture representation, and since the current through the light valve and therefore the opening of the light valve varies in accordance with this change in phase of the image modulated carrier wave, it is apparent that a positive picture corresponding to the negative at the transmitting station is produced on the image receiving surface mounted on the drum 14.

In the embodiment of the invention shown -in Fig. 2, carrier current lfrom source 30 and image current set up by the photoelectric cell 31 are impressed on a phase modulator 32, and the phase modulated Wave produced therein is transmitted over transmission channel 33 to the receiving station where it is amplified by amplifier 29 and impressed on light valve 34. Carrier current from source 30 is transmitted over a second channel 35 to the receiving station where it is amplified by amplifier 36 and impressed on light valve 37.

The light valve 37 opens and closes gradually over each cycle of the carrier current in accordance with the instantaneous values of its am litude. This is indicated diagrammatica ly by the curve 38 of Fig. 4. As shown by the curve 39 of Fig. 4, the valve 34 opens abruptly only for a short period during each cycle. This ma be accomplished by suitably designing the llght valve so that it does not transmit light if the actuating current is less in amplitude than a certain value near the peak value of the phase modulatedcurrent impressed upon it. The periodic opening of the light valve 34 may also be realized by connecting it directly in the output circuit of a vacuum tube, the grid of which is so biased that no current flows inthe anode circuit thereofk except when the hase modulated wave im pressed on its is near its maximum value. When the light valves 34 and 37 are operating as just described, the valve 34 o ens a given amount once during each cycle, ut the time at which the opening occurs varies with respect to thetime when the valve 37 is at its maximum opening. For instance, at position A, indicated in Fig. 4, the valve 34 is open when the valve 37 is closed and thus no light from source 38 is transmitted to the picture /receiving surface. At position B, valve 34 is open when valve 37 is near its maximum opening, thus permitting a maximum amount of light to reach the picture receiving surface. At position C, valve 34 is open when valve 37 is open an amount intermediate the maximum and minimum amounts. In this manner, the exposure of the light sensitive picture receiving surface is varied in accordance with the phase variations of the received phase modulated carrier wave.

The embodiment of the invention shown in Fig. 3 is the same as that shown in Fig. 2 with the exception that the light source 38 of constant intensity and the light valve 37 shown in Fig. 2 are displaced by a light source 40 which is connected to the output circuit of glow discharge lamp Y in accordance with the instantaneous values of amplitude of the carrier current from source 43 transmitted over channel 42 and amplifed by amplifier 41. In this case the time in which light valve 44 opens varies with respect to the timeat which the light emitted from the light source 40 is at its maximum'intensity.

One arrangement for producing a' phase modulated wave is disclosed in Patent No. 1,633,016- granted to'R.l V. L. Hartley, June 21, 1927. Another such arrangement is shown in Fig. 5. In this figure a photoelectric cell 50 is connected in series withbattery 51 and resistance 52. The varying potential difference across the resistance 52 due to the variation in the light actuating the photoelectric cell 50, is impressed differentially on the control electrodes of the similar electron discharge devices 53 and 54l so that the output impedance of one of the discharge devices is increased when that of the other discharge device is decreased and vice versa. A biasing battery 60 is employed so that the control electrodes of the two electron discharge devices will be biased equally, and therefore so thatl these devices will have the same output impedance, when the photoelectric cell is not circuits of the electron discharge device 54 connected in series. It is apparent that the current components reach? ed to a transmlssion channel actuated by light. A 'resistance 55 and battery 56 are in a common ortion' ofthe anode discharge 'devices 53 resistance elements each of these anode and 54. One ofthe equal 57 and 58-is connected in circuits. connected across resistance element 57 through an inductive reactance element 61 while the same current source is connected across resistance element 58 through a capacitative reactance element 62. The potential difference across element /is impressed on the input circuit of an electron discharge device 63, the output circuit of which is connect- 64 through transformer 65. The current from the source 59 travels by two paths. v One path is through the inductive reactance element 61 and. resistance 57, said`resistance element having in. shunt therewith the resistance element 55 and the output impedance of electron dischargeY device 53 connected in series. The other path is through the capacitative reactance element 62 and resistance element 58, said resistance having in shunt therewith the resista-nce element 55 and the output impedance of electron ing the' resistance element 55 by way of Y these two paths, respectively, are out of phase A and the electromotive force impressed on the input circuit of electron discharge device 63 is proportional to the vectorl sum of these components. L As the photoelectric cell 50 is acling means may be used to A source of carrier current 59 is r/ 4. In an electro-optical lmage producm phase 1ny accordance or scanning an object for Y corresponding change in the phase of the current transmitted over channel 64.

It is apparent that the term light controldesignate light valves such as indicated by the numerals 25, 34 and 37 and also sources of light such as the glow discharge lamp 40. Obviously, the glow discharge lamp 40 control the light reachinfr g the light sensitive and the light valves,

image receiving surface mounted on drum 14 ,for controlling the production of the image.

What is claimed is:

1. An4 electro-optical'image producing system comprising means for producing an electric wave which is modulated with respect to phase in accordance with the tone values of elemental areas o'f an object an image of which is to be produced, and means responsive to said phase for controlling the production of saidv image.

2. An electro-optical image producing system comprising a source of carrier current of substantially constant frequency, means for modulating said current with respect to phase in accordance with the tone values of elemental areas of an object, and means actuated jointly b frequency an said phase modulated current for producing an image of said object.

3. An electro-optical image producing system comprising a source of carrier current of substantially constant frequency, means for modulating said current with respect to phase in accordance with the tone values of elemental areas of an object, and a plurality of light controlling means forcontrolling the light utilized in the production of the image,

one of said controlling means being controlled by unmodulated current of said fre uency and another by said phase modulate current for producing an image of said object. system, a source of carrier current, means for scanning an object for producing an ima e current which varies in accordance with t e tone values of successively scanned elemental areas of said object, and means for modulating .said carrier current with respect to sald image current.

5. In an electro-optical image producing s stem, a source of carrier current, means producing an image current the amplitudeaof which varies in accordance with the tone values of the success'ively scanned elemental areas of said object, means for modulat rent with respect to phase 1n accordance with said carrier cur` unmodulated current of said los I with the variations of 00 modulated electric wave imag transmitting station,

- the light from -thereby producing an Vof which varies 1n lsaid source with respect to phase 1n accordance with the tone values of elemental areas of an object an image of which is to be produced, and means including a device for emitting light of an intensity which varies in accordance with the instantaneous values of said carrier current and a second device for transmitting light for a short interval during each cycle of said phase modulated current for controlling the production of said e In an electrooptical image producing station and a receivcarrier current at said means for modulating the carrier current from said source with respect to phase in accordance with the light tone values of the elemental areas of an object an image of which is to be produced, light controlling means at said receiving sta- 7 system, a transmittin ing station, a source o tion responsive to said phase modulated cury,

rent, a second light controlling means responsive to said unmodulated carrier current, and means including said two light controllin means for controlling the production o an image of said object.

8. In an electro-optical image producing system, a light sensitive device, a-source of light for actuating said light sensitive' device, means for controlling the intensity of said source reachin said light sensitive device in accordance with the tone values of the elemental areas of an object an image of which is .to be produced, image current in said light sensitive device, a source of constant requenc current, means for shifting the 'hase Ao; the constant frequency current m said source in accordance with the amplitudewariations of said image current, therebyf'prodilci'ng a phase modulated curren`t,'aA secondaccordance with the instantaneous values of the amplitude of the unmodulated constant frequency current from said source, and means responsive to said hasemodulated current for controllin t e intensity of the light from said secon source which reaches the position at whichv the image is to be produced'. A

9. In .an electro-optical image producing I source of light the -intensity tromotive forces on the anodes of said electron A discharge devices, said electromotivev forces being of the same frequency but different in phase, and means connected to a common portion o the anode circuits of said electron discharge devices for producing a light beam which varies in intensity in accordance with the intensity variations ot the light reaching said light sensitive device.

10. The method of producing an image of an object electro-optically which comprises producing a carrier wave, modulating said carrier wave with respect to 'phase in accordance with the light tone values of the elemental areas of said object and controlling the light tone values of the image of said object in accordance with the phase relation between said unmodulated carrier wave and said phase modulated carrier wave.

' 11. The method of producing an image of an object electro-optically which comprises modulatingfa carrier wave with respect to phase in accordance with the light tone values of successively scanned elemental areas of an object, an ima e of which is to be produced, controlling t e intensity of light in accordance with the instantaneous values of amplitude of said carrier wave, transmitting said light periodicallyv duringa portion of each cycle of said carrier wave determined in accordance'with the phase relation between said carrier wave and said phase modulated wave and utilizin said transmitted light for controlling tIie light tone values of the elemental areas of said image.

In testimony whereof, I have signed my name to this specication this 9th day of 

